JP3322926B2 - Manufacturing method of molded body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a molded product by using a raw material in the form of powder and granules, adding a liquid additive, obtaining a preformed product by a uniaxial pressing method, and further obtaining a molded product by a firing step. About the method.

[0002]

2. Description of the Related Art Conventionally, when a molded body is manufactured using raw materials in the form of powder and granules, a uniaxial pressing method, a hydrostatic pressing method, and the like are used to form a preformed body into a predetermined shape before a firing step. There is known a method of performing a hydrostatic pressing state using a molding method (CIP) or a uniaxial pressing method.

Accordingly, Japanese Patent Application Laid-Open No. H4-211 by the present applicant has been proposed.
As disclosed in Japanese Unexamined Patent Publication No. 904, a mixture obtained by adding a liquid additive to a raw material in the form of a granular material in advance is subjected to a molding treatment by a uniaxial pressure molding method while passing through an isostatic pressing state, thereby forming an excess liquid. A method of obtaining a preform by discharging the additive has been proposed. As a result, a preform having a uniform density and having an open pore state capable of excluding residual liquid and gas is formed, and the strength and density of the preform obtained by firing the preform are improved and homogenized. This has the effect of achieving the following.

[0004]

By the way, in recent years, raw materials have been made finer, that is, raw materials having a particle size of μm to submicron or less have been used.
It is desired to obtain a preform using such a raw material. However, when the raw material is finely divided, it is necessary to narrow the mold clearance for obtaining the preform from 70 μm to 100 μm from the conventional 70 μm to 100 μm to 10 μm to 30 μm. It will be huge. Furthermore, if the rheological properties of the raw materials and the liquid additive are thixotropic, leakage from the mold clearance will be significant. In addition, since the raw material and the liquid additive are mixed in advance, the fluidity of the mixture is deteriorated, and there is a possibility that a considerable amount of time may be required for filling the mold.

The present invention solves this kind of problem. Particularly, when preforming a finely divided raw material, the raw material is prevented from leaking and the filling time in a mold is reduced. It is an object of the present invention to provide a method for producing a molded article capable of producing a molded article having excellent strength and quality.

[0006]

In order to achieve the above object, the present invention provides a first preform by applying a first forming pressure to a powdery raw material by a uniaxial pressing method. First
A step of adding a liquid additive to the first preform obtained in the first step, and a step of uniaxial pressing to the first preform to which the liquid additive has been added. A third step of applying a second molding pressure greater than 1 molding pressure to obtain a second preform while removing excess liquid additives;
A fourth step of firing the second preform obtained in the third step to obtain a formed body.

Preferably, the first molding pressure is set within a pressure range of 20% to 95% of the second molding pressure.

Further, in the third step, the first preformed body is pressed by a uniaxial pressing method through a hydrostatic pressing state with the second forming pressure within its elastic deformation pressure range, and Preferably, two preforms are obtained.

Further, it is preferable that a part of the liquid additive added in the second step is previously added to the raw material before the first preform is obtained in the first step.

[0010]

In the method for producing a molded body according to the present invention, when the first molding pressure is applied to the granular raw material by the uniaxial pressing method to obtain the first preformed body, the cavity of the molding apparatus is constituted. Sliding occurs between the respective particles of the raw material in the gap between the punching wall and the punch, and a granular bridge in which respective vertices and ridges are cross-linked is formed. For this reason, it is possible to prevent especially the raw material in the form of fine particles from being discharged from the mold clearance to the outside. Next, a liquid additive is added to the particulate bridge, and a second molding pressure greater than the first molding pressure is applied by a uniaxial pressure molding method to remove excess liquid additive and to form a second preformed body. Is obtained. Therefore, the hydrostatic pressurized state is continued through the liquid additive that has permeated into the first preform through the gap of the granular material bridge, and uniform pressure is applied to all parts of the first preform. A second preform of uniform density is obtained.
Then, by firing the second preformed body, a desired formed body is obtained.

Here, the first molding pressure is equal to the second molding pressure of 2
When the pressure is 0% or less, the strength of the first preform decreases, and when the second preform is obtained by adding the liquid additive to the first preform, the raw material flows out together with the liquid additive. This makes molding impossible. On the other hand, when the first molding pressure becomes 95% or more of the second molding pressure, the second molding pressure is increased.
Defects such as cracks occur in the preform.

Further, when obtaining the second preformed body, the first preformed body is pressed by a uniaxial pressing method through a hydrostatic pressing state at a second forming pressure within its elastic deformation pressure range. Thus, a second preform in an open pore state capable of removing the residual gas is obtained, and the residual gas is discharged in the firing step, so that a high-density molded body can be obtained.

Before obtaining the first preform, a part of the liquid additive, for example, an amount of the raw material which is previously added to the raw material so as not to flow out by the mold clearance, is added to the first preform. You can also get

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for producing a molded article according to the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1, reference numeral 10 indicates a molding apparatus for producing first and second preforms for obtaining a molded body. The molding apparatus 10 includes a mold 12, and a cavity 14 is formed in the mold 12. Cavity 14
Is provided with a lower punch 16 and an upper punch 18. The lower punch 16 and the upper punch 18 are configured to press the raw material 20 sealed in the cavity 14 in a uniaxial direction (arrow direction). Have been. EXPERIMENTAL EXAMPLE 1 In the method for producing a molded body according to Experimental Example 1, first, 50% by weight of aluminum oxide powder (average particle diameter 0.4 μm), 40% by weight of titanium carbide powder (average particle diameter 1.4 μm), oxidation A powder material composed of 10% by weight of yttrium powder (average particle size: 0.6 μm) was sufficiently mixed using water as a dispersion medium. Further, 0.2 parts by weight of an ammonium alginate solution (0.2% solution) and 0.2 parts by weight of an acrylic resin emulsion are added as dispersants to 100 parts by weight of the powder material, and water is used as a dispersion medium. did.

Next, the powder material was defoamed for a certain period of time, then dried at 110 ° C. for 3 days, pulverized and sieved to produce a powdery raw material 20 having a size of about 150 μm or less.

Therefore, the raw material 2 thus obtained is
0 is filled in the cavity 14 of the molding apparatus 10 (FIG. 2).
A), the lower punch 16 and the upper punch 18 were press-formed at a pressure of 50 MPa (first forming pressure) by a uniaxial pressing method to obtain a first preform 22 (see FIG. 2B).

Next, the upper punch 18 is removed, 34 ml of purified water is added into the cavity 14 (see FIG. 2C), and the first preform 22 is subjected to the uniaxial pressure molding method by applying the first molding pressure. A second molding pressure, which was also changed from 60 MPa to 200 MPa, was applied to obtain a second preform 24 of 22.5 × 74 × 10 mm (see FIG. 2D). The result is shown in FIG. Here, the second molding pressure is 60
No cracks, cracks, or the like, which are molding defects, were observed in any of the second preforms 24 changed from MPa to 200 MPa.

Next, the second preform 24 is placed at 165
The temperature was raised to 0 ° C. to perform a sintering process. Here, when the second molding pressure was 200 MPa, fine hair cracks were observed.

In this case, as shown in FIG. 1, when the first molding pressure is applied to the raw material 20 filled in the cavity 14 by the uniaxial pressing method, the powder and granules constituting the raw material 20 and the gold Since the frictional resistance with the wall surface of the mold 12 is greater than the frictional resistance between the granular materials, the flexibility of the granular material in the central portion becomes better than the portion near the metallic mold 12. Therefore, the largest stress is applied to the edges 20a to 20d of the raw material 20, and the densification of the powders starts from the edges 20a to 20d.
The bridges are formed by bridging the granules connected by densification between the molds 20 to 20d and the wall surface of the mold 12. The bridge portion prevents the powder and granules constituting the raw material 20 from flowing out to the cavity 14 side.

The purified water added to the first preform 22 is supplied from the gap of the bridge portion to the first preform 2.
2 is applied to the first preformed body 22 by the uniaxial pressing method, excess purified water is discharged from the gap of the bridge portion, and an appropriate amount of residual purified water is discharged. A uniform pressure is applied to all parts of the first preform 22 by the purified water through a hydrostatic pressure state. As a result, a second preform 24 having a uniform density is obtained. In addition, since the second molding pressure is set to a pressure within the elastic deformation pressure range of the first preformed body 22, the second preformed body 24 maintains an open pore state. Therefore, if sintering is performed on the second preformed body 24, the residual gas inside the second preformed body 24 is discharged, and pores can be eliminated after firing, so that a high-density formed body can be obtained. Becomes possible.

In the first embodiment, purified water is added to the cavity 14 after the first preformed body 22 is obtained by the uniaxial pressure molding method. When filling the cavity 14 with the 20, a part of the purified water, for example, the raw material 20 is added by an amount that does not flow out of the clearance of the mold 12, and the remaining purified water is added after the first preform 22 is formed. It may be added. Comparative Example 1 Using a powder having the same composition as in Experimental Example 1 and subjected to the same treatment, preforms were obtained by changing the pressing force from 60 MPa to 200 MPa by a commonly used dry pressing method. Was. The results are shown together with Experimental Example 1 in FIG. In this conventional method, the pressing force is 90 MPa.
Gave a relative density of about 50%. Cracks were observed in the preformed body having a pressing force of 100 MPa. Further, in the preformed body having a pressing force of 120 MPa, a part of the preformed body was peeled off, and the pressing force was reduced to 15 MPa.
In the case of the 0 MPa preform, cracks and peeling occurred so that the preform could not be taken out of the mold while maintaining the predetermined shape.

Next, the preform was fired under the same conditions as in Experimental Example 1. At that time, cracks were observed parallel to the thickness direction in the preformed body having a molding pressure of 90 MPa or more. Particularly, in the case of using a powder to which a dispersant or a binder was added, the occurrence of cracks was more remarkably observed. Was. Experimental Example 2 In the method for manufacturing a molded body according to Experimental Example 2, aluminum oxide powder (purity: 99.9%, average particle size: 0.4 μm) was prepared as shown in FIG.
A, as shown in FIG.
0.018MPa (Upper punch 1
The first preforming body 22 was formed by applying a first forming pressure that was changed stepwise between the pressure of 8 (self weight 8) and 116 MPa (see FIG. 2B). Furthermore, after removing the upper punch 18 and adding 35 ml of alcohol to the cavity 14 (see FIG. 2C), the upper punch 18 and the lower punch 16 are applied with a second molding pressure maintained at 120 MPa by a uniaxial press molding method. In the same manner as in Experimental Example 1, the second preform 2
4 was obtained (see FIG. 2D).

In this case, in Experimental Example 2, when the first molding pressure is 10 MPa or less, the powder flows out of the cavity 14 together with the alcohol when the second molding pressure is increased to 120 MPa in order to obtain the second preform 24. And
The desired second preform 24 could not be formed. On the other hand, when the second preformed body 24 is formed using the first preformed body 22 obtained by setting the first forming pressure to 24 MPa, while the second forming pressure of 120 MPa is applied, the powder No spill, only alcohol.
Thereafter, the complete second preform 24 was obtained until the first molding pressure reached 116 MPa.

Similarly, the first molding pressure is set to one of the second molding pressure.
The pressure was changed stepwise from 8% to 96.5%, and the second molding pressure was set to 100 MPa and 180 MPa to form the second preform 24.

Here, when the second molding pressure is 100 MPa, the outflow of the powder occurs when the first molding pressure is 18% of the second molding pressure, and the outflow of the powder is avoided when the first molding pressure is 20%. . On the other hand, when the second molding pressure was 180 MPa, even when the first molding pressure was 18% of the second molding pressure, the powder did not flow out, and a good second preform 24 was obtained. .

Next, the various second preforms 24 obtained as described above were sintered at 1650 ° C. In this case, when the second molding pressure is 100 MPa and 120 MPa,
No defects were found in the first molding pressure up to 95% of the respective second molding pressure, and the
Hair cracks were observed at a pressure of 96.5% of the molding pressure. When the second molding pressure is 180 MPa,
Hair cracking was observed when the first molding pressure was 95% of the second molding pressure.

From these results, the relationship between the first molding pressure and the second molding pressure was set as shown in FIG. Therefore, it is confirmed that if the first molding pressure is set within a pressure range of 20% to 95% of the second molding pressure, there is no outflow of powder or cracks, and a good molded body can be obtained. Was. EXPERIMENTAL EXAMPLE 3 In the method for producing a molded body according to Experimental Example 3, a powder material composed of 99% by weight of electrolytic copper powder (average particle diameter of 20 μm) and 1% by weight of metal chromium powder (average particle diameter of 6.5 μm) was sufficient. Was mixed. Next, the powder material is transferred to the cavity 14 of the mold 12.
And a first forming pressure of 75 MPa was applied by a uniaxial pressing method, whereby a first preform 22 was obtained.

Further, the upper punch 18 is released and the cavity 14 is filled with a 50% solution of titanium isopropoxide for 7 minutes.
After the addition of 0 ml, a second molding pressure of 150 MPa is applied to the second preform 2 of 25 × 140 × 40 mm.
4 was obtained.

Next, the second preformed body 24 was sintered in a nitrogen atmosphere to obtain a formed body. This molded product has a theoretical density ratio of only sintering of 98.7% or more, and a fine TiO 2
₂ was a dispersed alloy.

[0031]

As described above, in the method for producing a molded article according to the present invention, particularly when a raw material composed of fine particles is used, or when the rheological properties of the particles and the liquid are thixotropic. However, the first preformed body having a low density is first formed using only the raw material composed of the granular material. For this reason, even if the liquid additive is added to the first preformed body, the first preformed body does not flow, and further, the second preformed body having a uniform density in all parts through the hydrostatic pressure state. A molded article can be obtained. Further, the first preform is pressurized in a pressurized state within its elastic deformation pressure range, and is formed while excluding liquid, so that a liquid separation path remains, and an open pore state capable of excluding residual gas is formed. A second preform can be obtained, and the second preform can be fired to produce a molded product having excellent strength and quality. In addition, the degreasing step before firing is not required, and the efficiency of the entire manufacturing process is improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a molding apparatus used when carrying out a method of manufacturing a molded article according to the present invention.

FIG. 2 is a schematic diagram when a first and a second preform are molded by the molding apparatus.

FIG. 3 is a diagram showing a relationship between a molding pressure and a relative density according to the present embodiment and a conventional technique.

FIG. 4 is a diagram illustrating a relationship among a first molding pressure, a second molding pressure, and a relative density in the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Molding apparatus 12 ... Die 14 ... Cavity 16 ... Lower punch 18 ... Upper punch 20 ... Raw materials 22, 24 ... Preform

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI B30B 11/02 B30B 11/02 Z (72) Inventor Naoki Ota 1-10-1 Shinsayama, Sayama City, Saitama Honda Engineering Co., Ltd. (72) Inventor Mitsuhiro Funaki 1-10-1 Shinsayama, Sayama City, Saitama Prefecture Honda Engineering Co., Ltd. (56) References JP-A-4-211904 (JP, A) JP-A-1-287203 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B28B 3/02 B28B 3/00 102 B30B 11/00 B30B 11/02 B22F 3/02

Claims (4)

(57) [Claims] 1. A first step of applying a first forming pressure to a granular material by a uniaxial pressing method to obtain a first preformed body; and a first preforming obtained in the first step. A second step of adding a liquid additive to the body, and applying a second molding pressure greater than the first molding pressure to the first preformed body to which the liquid additive has been added by a uniaxial pressing method, and A third step of obtaining a second preformed body while removing the liquid additive of the above, and a fourth step of firing the second preformed body obtained in the third step to obtain a formed body. A method for producing a molded article characterized by the following. 2. The method according to claim 1, wherein the first molding pressure is set within a range of 20% to 95% of the second molding pressure. . 3. The manufacturing method according to claim 1, wherein in the third step, the first preform is subjected to a hydrostatic pressing state by a uniaxial pressing method, and the second preform within an elastic deformation pressure range thereof. A method for producing a molded article, characterized in that the second preformed article is obtained by applying pressure at a molding pressure. 4. The manufacturing method according to claim 1, wherein a part of the liquid additive added in the second step is removed before the first preform is obtained in the first step. A method for producing a molded article, wherein the molded article is added in advance to the raw material.